In recent years, rechargeable battery devices used for personal computers, mobile terminal devices such as mobile phones, video cameras, satellites, vehicles, and the like are actively developed. Such rechargeable battery devices include secondary batteries, such as lithium ion batteries that can be made ultra thin and can have a small size. As secondary battery packaging materials used for such batteries, laminated packaging materials are attracting attention. The laminated packaging materials are formed of multilayer films (having a configuration, for example, of substrate layer/first adhesive layer/aluminum foil layer/second adhesive layer/heat-sealable resin layer). Unlike metal cans conventionally used as containers, such laminated packaging materials formed of multilayer films have a light weight and high heat dissipation properties and can shapes can be freely selected, and therefore, are improved or even superior to metal cans.
Such laminated packaging materials are roughly classified into two types on the basis of the methods of preparing a second adhesive layer between an aluminum foil layer and a heat-sealable resin layer. In other words, the laminated packaging materials are roughly classified into ones having a dry lamination structure in which a second adhesive layer is prepared by means of a dry lamination method, and ones having a heat lamination structure in which a second adhesive layer is prepared by means of an extrusion lamination method.
Those secondary battery packaging materials which have a dry lamination structure can be simply manufactured by means of a dry lamination method commonly used in manufacturing packaging materials, for example. Therefore, the secondary battery packaging materials having a dry lamination structure generally have a short period of use, and thus are used for consumer-oriented applications, such as portable devices, which are desired to be at low cost.
On the other hand, the packaging materials having a heat lamination structure are manufactured through more complicated processes using an extrusion lamination method, for example. Thus, the packaging materials having a heat lamination structure generally have a longer period of use, and thus are used for industrial applications, such as electric vehicles, motorbikes and power assisted bicycles, which are desired to have high reliability.
As batteries using laminated packaging materials, two types of packaging modes are proposed for sealing battery contents. Battery contents include, for example, a positive electrode, a separator, a negative electrode, an electrolyte solution in which an electrolyte is dissolved, and tabs each formed of a tab lead and a tab sealant. The two modes are:
(1) Pouched type packaging modes in which a pouch is formed using a packaging material and battery contents are accommodated in the pouch.
(2) Embossed type packaging modes in which a packaging material is cold-molded to form a recess and battery contents are accommodated in the recess.
The embossed type packaging modes include a mode for more efficiently packaging contents by forming a recess in both of the packaging materials to be stuck to each other to increase an accommodation volume and thus increase the battery capacity. For example, there is a laminated type battery in which two packaging materials having a recess formed by cold molding are heat-sealed, with the battery contents being sandwiched between the recessed materials. The battery contents at least include a positive electrode, a separator, a negative electrode, an electrolyte solution in which an electrolyte is dissolved, and tabs each formed of a tab lead and a tab sealant.
Recently, laminated packaging materials are desired to have various properties, such as sealing properties, chemical resistance, deep drawing properties, water vapor barrier properties, heat resistance, and insulating properties. In particular, the currently used packaging materials having a dry lamination structure are desired to improve properties associated with long-term reliability, such as chemical resistance, heat resistance, and water vapor barrier properties, compared with the laminated packaging materials having a heat lamination structure.
For example, PTL 1 discloses a battery case packaging material including an oriented heat-resistant resin film layer as an outer layer, a non-oriented thermoplastic resin film layer as an inner layer, and an aluminum foil layer disposed between these layers. The non-oriented thermoplastic resin film layer is adhered to the aluminum foil layer via an adhesive layer that contains polyolefin having a carboxyl group and a polyfunctional isocyanate compound. Thus, the chemical resistance or moldability of the battery case packaging material is ensured.